Detection of malignant processes in sufficient time to allow successful treatment of disease is the major challenge to diagnostic medicine. In an effort to meet that challenge, this project proposes the exploration of the tumor and nodal delineating capabilities and melanin binding potential of a series of water-soluble porphyrins, pseudo-porphyrins and their indium and gallium chelates. The porphyrins have long been known to exhibit a special affinity for certain tissues and organs, and unique affinities have recently been demonstrated for some water-soluble porphyrin derivatives. The synthesis, characterization and in vitro and in vivo evaluation of these compounds will be coupled with an assessment of the interrelationship of their physical, chemical and electronic properties and their observed behavior in melanin binding and tissue distribution studies. The first free base reduction potential of the free ligand and the first reduction potential of the complexes will be determined and the role this property plays in the binding and localization of the compounds assessed. These studies will result in the development of predictive tools to aid in the future design of more efficient imaging agents and may thereby also provide increased insight into the nature of the malignant process.